Garbage is a major environmental problem, especially now for urban centers. Typically garbage is collected from various premises and taken to a disposal site. Often such disposal sites are landfill sites, where the garbage is essentially dumped into a hole in the ground. However, the disposal of such garbage is a major environmental concern. Landfill disposal sites are expensive to operate and tend to fill up over time, thus needing to be replaced. Rising land costs have made replacement of landfill sites expensive. Additionally, landfill sites may be environmentally hazardous, with chemicals, pollutants and the like leaching into the ground water supply.
Faced with the rising costs and concerns about landfill sites, the operators of such landfill sites have begun to dramatically increase the fee charged for disposing garbage at such sites. Typically now the fee charged is based on the weight of garbage disposed of. Thus, each refuse truck seeking to off-load garbage is weighed on the way into the landfill site and weighed on the way out of the landfill site. The weight difference is then calculated and a fee is paid in accordance with that weight difference.
Additionally, concerns have been raised about the total weight of individual vehicles which travel public roads. The greater the weight of the vehicle the greater the wear of the roadway. Weight restrictions have been imposed on many roadways and substantial fines may be payable for overweight vehicles. Also, the land fill site records can be used as evidence of overweight violations by the appropriate regulatory agency. Both of these trends, namely increased costs of dumping and increased overweight fines, increase the importance for refuse truck operators being able to know the total weight of the refuse being carried in their trucks, and the incremental weight being added by each additional pickup.
In a typical refuse operation, a customer signs a contract which guarantees that a refuse receptacle will be emptied on a periodic basis. However, the contract is typically based upon a flat fee and does not take into account the actual weight of refuse to be removed from the site. The weight of the refuse may vary with demolished building materials being very heavy whereas cardboard packing or paper packing products are very bulky, but light. The refuse hauler pays to dump the refuse at the landfill or other disposal site based upon the weight of refuse being disposed. However, the customer is charged on a flat fee for a given time, such as a week or month, resulting in customers with light refuse being overcharged, while customers with heavy refuse are undercharged. What is desired therefore, is a way for the refuse operator and the refuse-hauling companies to determine the weight of refuse being hauled from each customer's container each time. Preferably, such measurement device would enable the operator of the refuse vehicle to know also what the weight of the refuse of the truck at any given time was to avoid overloading the truck and thus being liable for over-weight fines.
There are several examples of past devices which attempt to provide the desired weight information. However, these prior devices all suffer from various unsuitabilities. For example, there are devices which require that the lifting, emptying and return cycle for emptying a container into the refuse truck be interrupted so that a weight reading can be made. The stopping of the lifting and lowering motion of the container is unsuitable for several reasons. Firstly, there is a time loss associated with such a stoppage which is unacceptable. Secondly, the machinery used to effect the lifting is often quite powerful, but not very nimble. Thus, requiring the cycle to be stopped typically causes large vibrations, which may create excessive wear on the equipment and premature breakdown. Thus, devices which require the operation to be stopped in order to effect measurement are not suitable. Examples of such devices may be found in U.S. Pat. No. 4,645,081 to Garbade and German Publication 33 32 058.
Other devices have been proposed which involve vertical load cells upon which the container being weighed is placed. However, these also have a number of disadvantages. As indicated previously, the equipment while powerful often vibrates upon beginning or ending its motion. Thus, placing containers directly on vertical load cells is unsuitable, because it is difficult to protect the load cells from excessive wear by the rough use that such equipment typically gets. An example of such a device is again U.S. Pat. No. 4,645,081 and U.S. Pat. No. 4,714,122.
Other systems have proposed for example measuring the fluid pressure of the hydraulic cylinders, which are used to effect the lifting of the refuse containers. Examples of such systems include U.S. Pat. Nos. 4,771,837; 4,824,315; and 4,854,406. However, in each of these devices the pressure sensed is remote from the actual loading causing the pressure. Thus, other factors affect the pressure reading. Such factors include the amount of acceleration on any upward or downward swing and more importantly, the length of the moment arm between the centre of gravity of the weight being lifted and the pressure being sensed. The centre of gravity of any given refuse container may vary considerably depending upon how the refuse is placed in the container. Often, the container is loaded from one end, resulting in the centre of gravity of the refuse being closer to that end. In addition, the position of the container on the lifting forks may vary a certain amount. Thus, without knowing where the centre of gravity of the refuse-filled container is, it is impossible to accurately estimate the weight of the container simply by measuring the hydraulic cylinder pressure. Errors in estimating the weight of the container based on a measurement of pressure remote from the container may be in the order of 20-40%, if the centre of gravity is not at the assumed centre of volume, because of the moment arm involved. Further, the pressure reading in the hydraulic cylinder may not be an accurate representation of the lifting force. For example, viscosity effects which are temperature-dependent, and stiction which may be considered as the frictional resistance force within a hydraulic cylinder vary with temperature and pressure respectively. Thus, any system which attempts to accurately estimate weight should consider these effects also.
What is desired therefore, is a method of accurately determining the weight of a container being lifted, emptied and lowered without requiring the use of vertical load cells or the actual stopping of the lifting and lowering cycle, and which will determine the weight of the material dumped from the container into the refuse truck.